Modular units have been used to construct residential and industrial structures because they can be assembled at a factory and transported via train, truck or ship to a construction site for assembly into a multi-unit building thereby avoiding much of the delay and expense of field construction. To achieve the maximum benefit from the modular building it is important that modular units be constructed and interconnected in ways which maximize the strength of an assembled modular building, while minimizing the use of external framing and bracing which requires field construction. The interconnection of the box-shaped modules which are the basic building blocks of modular construction has been found to be a critical component in achieving the goals of modular construction.
Various connection systems have been used to enable multi-unit modular buildings to resist external forces, such as those imposed on a building by severe weather. Examples of such systems are disclosed in U.S. Pat. No. 3,831,332 to Weese and U.S. Pat. No. 6,871,453 to Locke. Weese's system links adjacent modular units using a central support column comprised of column segments which extend diagonally from the corner of each modular unit. Tension rods extend through Weese's central columns and are secured at the opposite ends of the columns to hold the column segments and their appended modular units together. Weese's system may be effective with a modular building of a few stories, but the structural strength of Weese's connection system is limited and the geometry of his system results in adjacent modular units being separated by a distance corresponding to the aggregate lateral projections of the column segments which extend from his modular units. The present inventors have determined that avoidable separation of the exterior load bearing walls of adjacent modular units is undesirable in that it tends to make a multi-unit modular structure less rigid and less capable of resisting external forces.
Locke's modular unit connection system utilizes connector bars having opposed upper and lower conical sections with an axial bore to join adjacent modular units. Structural members on Locke's modular units are equipped with conical recesses which are adapted to receive the conical sections at the ends of Locke's connector bars. Tensioner run through the axial bores in Locke's connector bars to hold vertically aligned modular units together. As with Weese's system, Locke's system results in a gap between adjacent modular units. It also suffers the detriment of requiring the fabrication of complex shapes for Locke's connectors and the recesses in the structural member which receive them.
The present invention relates to a novel system for constructing a building with box-shaped modular units. A principal object of the invention is to provide a system which enables the quick and efficient construction of high rise modular buildings having sufficient structural strength to resist the external forces associated with tall buildings and for which the connection work can be performed from the outside of the building's modules, thereby maximizing the amount of finish work that can be completed in the factory.